The invention relates to a display device comprising a flexible substrate with a matrix of pixels on the substrate, switching elements which are selectable by means of row electrodes for presenting data, which have been presented via column electrodes, to the pixels.
Examples of such active matrix display devices are the TFT-LCDs or AM-LCDs which are used in laptop computers and in organizers, but they also find an increasingly wider application in GSM telephones.
The use of such display devices in xe2x80x9cwhite paperxe2x80x9d applications is also increasingly considered. The display devices then have the appearance of a newspaper. Since the substrate is flexible, it can be partly or not partly folded. This flexibility also provides possibilities of applications in xe2x80x9cwearable displaysxe2x80x9d. Instead of LCDs, for example, organic or polymer LED display devices may be used alternatively.
However, problems may occur when the substrates are often bent or bent too much. To ensure a satisfactory flexibility, a polymer material such as, for example, polyaniline (PANI), polyethylene-dioxythiophene (poly-DOT), pentacene, poly(thienylene vinylene) (PTV) or poly-3-hexylthiophene (P3HT) are preferably chosen for all materials to be used, i.e. also for the materials for the column electrodes and the row electrodes, the insulating layers and the semiconductor materials.
A drawback of the use of polyaniline (PANI) as a conducting material is its high resistance; the sheet resistance is about 1,5.103xcexa9/(at a layer thickness of 200 nm). If this is used for a column conductor with a width of about 25 xcexcm and dimensions of the pixels in the direction of a column conductor of about 540 xcexcm, the resistance along each pixel is about 35 kxcexa9. The provision of a double layer of PANI with, for example, a metal may provide a solution, but the conventional materials adhere poorly to the PANI or are not very attractive for other reasons (etching rate differences). The structuring of a metal provided on an organic layer, or PANI is not possible in practice or causes great problems.
It is an object of the present invention to obviate this problem and to this end, the invention provides a display device with a flexible substrate, in which parts of the column electrodes are arranged parallel to mutually separate strips of a conducting material insulated from the column electrodes, or parts of the row electrodes are arranged parallel to strips of a conducting material insulated from the row electrodes.
The invention is based on the recognition that it is possible to provide a strip of a satisfactorily conducting material parallel to the high-ohmic column electrodes or row electrodes, which strip is, as it were, already broken in a defined way. The separate parts are then arranged parallel to the high-ohmic conductors via feed-throughs.
The strips of conducting material preferably have a dimension which, in the direction of the relevant electrode, is substantially equal to the dimension of the pixel in this direction, reduced by the width of an electrode in the direction transverse (perpendicular) thereto (at least in matrix with transversely crossing column electrodes and row electrodes).
Since the row electrodes are usually subjected to the heaviest capacitive load, the strips of a conducting material and the row electrodes are made of the same low-ohmic material in a preferred embodiment. Since they can be manufactured (bottom-gate configuration) on one level (directly on the substrate), a metal can be used for this purpose and no extra masking step is required.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.